Cellular communication systems are becoming increasingly more important. In such cellular communication systems, a user equipment (UE), such as a mobile phone or cellular computer modem, connects wirelessly to the network via base stations (BSs), that in turn are connected to a backhaul network for forwarding the communication from the user equipment.
UEs are normally equipped with transceiver circuitry for accessing cellular networks of different kinds using different radio access technologies (RATs). Examples of such RATs include GSM (Global System for Mobile communications), WCDMA (Wideband Code Division Multiple Access), and 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) system, in the following referred to simply as “LTE”. Such cellular RATs typically operate in various frequency bands in the range 0.5-5 GHz. In addition to the cellular RATs, UEs may also be equipped with transceiver circuitry for other types of RATs, such as Bluetooth, wireless local area networks (WLAN), near field communication (NFC), etc. Some emerging RATs, such as IEEE 802.11ad and WirelessHD, may operate in frequency bands that are located at significantly higher frequencies than e.g. the 0.5-5 GHz mentioned above, such as in the 60 GHz band.
For a UE with multiple RAT capability, there is a need to generate a multitude of local oscillator (LO) signals for transceivers of the different RATs. Furthermore, the range of LO frequencies that need to be generated may be relatively wide. Thus, there is a need for efficient frequency synthesizer circuitry for radio transceivers.